The present disclosure relates to processes and intermediates for preparing branched polycarbonates compositions. In this regard, the disclosure relates to the interfacial synthesis of branched polycarbonates and to compositions produced by such processes. Also included are articles, such as molded, extruded, thermoformed, etc. articles, formed from these compositions.
Polycarbonates (PC) are synthetic thermoplastic resins derived from bisphenols and phosgene, or their derivatives. They are linear polyesters of carbonic acid and can be formed interfacially from reaction of dihydroxy compounds with phosgene or via ester interchange by reaction of dihydroxy compounds with a carbonate diester.
The desired properties of polycarbonates include clarity or transparency (i.e. 90% light transmission or more), high impact strength and toughness, heat resistance, weather and ozone resistance, good ductility, being combustible but self-extinguishing, good electrical resistance, noncorrosive, nontoxic, etc. They are useful for forming a wide array of products, such as by molding, extrusion, and thermoforming processes. Branched polycarbonates, in some instances, can produce enhanced, or more desirable, characteristics over conventional linear polycarbonates.
In producing a polycarbonate, a homopolycarbonate is generally formed from the polymerization of a dihydroxy compound such as bisphenol-A. To form a branched polycarbonate, a branching agent which has at least three functional groups is added to the mixture. Exemplary branching agents include trimellitic trichloride and 1,1,1-tris(hydroxyphenyl)ethane (THPE). Typically, the branching agent is added during the reaction of the dihydroxy compound with phosgene. Because each functional group can react with a dihydroxy compound, branching occurs. However, one problem that arises from the use of a branching agent is high residual content of ionic groups, such as chlorides. High chloride content can adversely impact melt stability, hydrolytic stability, and possibly the color and/or transparency of articles molded from the polycarbonate.
It is desirable to generate new processes that allow the formation of branched polycarbonates without high residual ionic content. Included therein are processes for producing relatively transparent, flame-retardant polycarbonates capable of providing good flame retardance characteristics in thin wall constructions.